Standard computer monitors and TV displays are typically based on three additive primaries: red, green, and blue, collectively denoted RGB. These monitors may not be able to display many colors perceived by humans, since they are limited in the range of color they are capable of displaying. FIG. 1A schematically illustrates a chromaticity diagram as is known in the art. The closed area in a shape of horseshoe represents the chromaticity of colors that can be seen by humans. For each chromaticity, described as a point on the two-dimensional plane, different levels of brightness are possible, thus constructing a three-dimensional color space. The points on the border of the horseshoe, known as the spectrum locus, correspond to monochromatic excitations in the range from 400 nm to 780 nm as marked. A straight line closing the horseshoe from below, between the extreme monochromatic excitation at the long and short wavelengths, is named the purple line. All colors discernible by human eye are inside this closed area, which is called the color gamut of the eye. The triangular area enclosed by the color gamut in FIG. 1A represents the range of colors that can be produced by a standard RGB monitor. The area of the color gamut outside the RGB triangle indicates that many colors seen by humans are not discernible on standard monitors.
Existing display devices can be divided into two groups, namely, direct view devices and projection devices. The direct view devices group includes CRT, LCD, LED and other displays. In direct view devices, each display is composed of three-color sub-pixels, namely RGB, which are physically located at the screen. The color image is created by the viewer's visual system which mentally integrates the colored light arriving from spatially neighboring sub-pixels to give a full color impression.
The light emission mechanism may be different in the different types of devices. In a CRT display, an electron beam accelerated by a scanning electron gun cause the different color phosphors at the screen to emit visible light. In LED devices, different color LED pixels are directly driven by electric current to emit light. In both cases the strength of the excitation determines the intensity of the emitted light. The input data modulates the intensity of the excitation of different pixels to create a desired image.
In LCD devices, color is created by filtering white light through an array of red, green and blue optical filters, which correspond to red, green and blue sub-pixels. The transparency of different color is modulated by an array of LC elements, which is placed juxtaposed and in registry with the color filter sub-pixel array. The transparency of the LC array cells, which control the intensity of respective sub-pixels, is modulated by controlling the voltage applied to the cells. These voltages are modulated in accordance with the input data to create the desired image.
Projection display systems create images by projecting light on a viewing screen. There are generally two types of projection display systems, namely, simultaneous displays and sequential displays. Simultaneous projection display systems are based on projecting light of all three primaries simultaneously onto to the viewing screen, whereby color combinations are perceived by spatial integration of the colors by the visual system of the viewer. Sequential projection display systems project separate images of the different primary colors onto the screen sequentially, at a sufficiently high frequency so that the human eye can perceive color combinations by temporal integration of the primary color images.
Standard video data is typically transferred in YCbCr or RGB related formats. The data is encoded, either digitally or analogously. Color is represented in a three-dimensional space suitable for presentation on a three-primaries monitor or display. The input data in YCbCr format is translated, using a conversion matrix, to corresponding RGB data. If RGB input data is used the matrix conversion is not required, and the input RGB data is passed directly to the monitor. Signals responsive to the RGB data are used to drive the three-primaries display. The RGB data includes R, G and B signal components (channels): the R signal component represents the red primary; the G signal component represents the green primary; and the B signal component represents the blue primary. Three multipliers and/or one-dimensional look-up tables, one for each of the RGB channels, are used to adjust color temperature and other responses of the system. Certain processes can also be applied to the original YCbCr data, controlling the visual appearance using the YCbCr coordinates. For example, the Y channel might be manipulated in order to control the brightness and the contrast of the image. Alternatively, the Cb and Cr data can be manipulated to control the color saturation of the final image. A user of the display may perform such manipulations and adjustments, e.g., by adjusting the “brightness”, “contrast” and “color” of a display monitor.
As described above, existing display monitors reproduce colors only within a limited portion of the full color gamut of the eye. Therefore, to improve image reproduction quality and richness, there is a need for a display monitor capable of reproducing a wider color gamut, including color ranges beyond the enclosed triangular area in FIG. 1A.